JP7184725B2 - working machine - Google Patents

Description

The present invention relates to working machines such as hydraulic excavators.

A working machine such as a hydraulic excavator includes a hydraulic actuator, a hydraulic pump driven by a prime mover, a control valve that controls the flow of pressure oil from the hydraulic pump to the hydraulic actuator, and an operating device that operates the control valve. The operation device has, for example, an operation lever that can be operated by an operator, and a pilot valve that generates pilot pressure according to the amount of operation from the neutral position of the operation lever. output to the pressure receiving part. This switches the control valve from the neutral position to the switching position. As a result, the hydraulic actuator is driven by supplying and discharging pressurized oil through the control valve.

The open center type control valve has a meter-in opening for supplying pressure oil from the hydraulic pump to the hydraulic actuator, a meter-out opening for discharging the pressure oil from the hydraulic actuator to the tank, and a meter-out opening for discharging the pressure oil from the hydraulic pump. and a bleed-off opening for returning to the tank. In the neutral position of the control valve, for example, the meter-in and meter-out openings are closed and the bleed-off opening is open to return pressurized oil from the hydraulic pump to the tank. At the switching position of the control valve, for example, the areas of the meter-in opening and the meter-out opening increase and the area of the bleed-off opening decreases as the pilot pressure (that is, the amount of operation of the control lever) increases. As a result, pressure oil is supplied to and discharged from the hydraulic actuator, and the flow rate is controlled.

The working machine described in Patent Document 1 includes a bleed-off valve arranged in a bleed-off pipeline that returns pressure oil from a bleed-off opening of a control valve to a tank, a regulator that variably controls the displacement of a hydraulic pump, a pilot pressure ( That is, it includes a pressure sensor that detects the amount of operation of the operating device, and a controller that controls the bleed-off valve and the regulator according to the pilot pressure detected by the pressure sensor.

The controller controls the bleed-off valve so that the degree of opening (opening area) of the bleed-off valve decreases as the pilot pressure increases. Further, the controller calculates a reference pump flow rate based on the pilot pressure, corrects the reference pump flow rate based on the opening of the bleed-off valve, and adjusts the displacement of the hydraulic pump to correspond to the corrected reference pump flow rate. Control the regulator. As a result, compared to the case where the reference pump flow rate is not corrected, the pump flow rate is reduced, and energy can be saved.

Japanese Patent No. 5886976

However, there is room for the following improvement in the above conventional technology. For example, when the operating lever is quickly returned to the neutral position, the meter-in and meter-out opening areas of the control valve decrease and the bleed-off opening area increases, followed by an increase in the opening area of the bleed-off valve. As a result, the opening area of the bleed-off valve becomes temporarily insufficient, causing blockage of the pump pressure.

SUMMARY OF THE INVENTION An object of the present invention is to provide a working machine capable of preventing lock-in of pump pressure.

In order to achieve the above object, the present invention provides a hydraulic actuator, a variable displacement hydraulic pump driven by a prime mover, and an open center type control for controlling the flow of pressure oil from the hydraulic pump to the hydraulic actuator. a valve, an operation device for operating the control valve, an operation amount detector for detecting an operation amount of the operation device, a regulator for variably controlling the displacement of the hydraulic pump, and a signal supplied from the hydraulic pump to the control valve. a bleed-off valve arranged in a bleed-off pipeline for returning the pressured oil to the tank; and a controller that outputs a first command current and a second command current for controlling the opening of the bleed-off valve, wherein the second command current from the controller operates to bleed. An electromagnetic proportional valve that generates off control pressure is provided, the bleed-off valve is operated by the bleed-off control pressure from the electromagnetic proportional valve, and the opening area decreases as the bleed-off control pressure increases, The controller uses the operation amount of the operating device detected by the operation amount detector to calculate the rate of decrease of the operation amount, and when the rate of decrease of the operation amount is greater than a preset value, The second command current is corrected by multiplying a reduction factor smaller than 1 so that the bleed-off control pressure becomes smaller than when the rate of decrease of the manipulated variable is equal to or less than the predetermined value.

According to the present invention, blockage of pump pressure can be prevented.

It is a side view showing the structure of the hydraulic excavator in one embodiment of the present invention. It is a figure showing a hydraulic pump, a hydraulic actuator, a control valve, etc. of composition of a hydraulic drive in one embodiment of the present invention. It is a figure showing the operation device etc. of the composition of the hydraulic drive in one embodiment of the present invention. 3 is a block diagram showing the functional configuration of a controller in one embodiment of the present invention; FIG. FIG. 4 is a calculation table for the bleed-off control section of the controller in one embodiment of the present invention, showing the relationship between the pilot pressure and the bleed-off control pressure. FIG. 5 is a diagram showing operating characteristics of the bleed-off valve in one embodiment of the present invention, showing the relationship between the bleed-off control pressure and the opening area of the bleed-off valve. FIG. 4 is a calculation table of the reduction factor calculation unit of the controller in one embodiment of the present invention, and is a diagram showing the relationship between the rate of decrease of the pilot pressure and the reduction factor. 4 is a time chart showing the operation of the first comparative example, showing a case where the operating lever is returned to the neutral position; 4 is a time chart representing the operation of one embodiment of the present invention, showing a case where the operating lever is returned to the neutral position; 9 is a time chart showing the operation of the second comparative example, showing a case where the control lever is returned to the neutral position and the reduction factor temporarily increases; FIG. 10 is a diagram for explaining the operation of the embodiment of the present invention, showing a case where the control lever is returned to a neutral position and the reduction factor temporarily increases;

One embodiment of the present invention will be described with reference to the drawings.

FIG. 1 is a side view showing the structure of the hydraulic excavator in this embodiment. Hereafter, the front side (left side in FIG. 1), rear side (right side in FIG. 1), left side (front side in FIG. 1), and right side (in FIG. 1) of the operator who boarded the cab of the hydraulic excavator rear side) are simply referred to as the front side, the rear side, the left side, and the right side.

The hydraulic excavator of this embodiment includes a travelable traveling body 1 , a revolving body 2 rotatably provided above the traveling body 1 , and a working device 3 connected to the front side of the revolving body 2 . The traveling body 1 travels by being driven by a left traveling motor 4A and a right traveling motor 4B (see FIG. 2, which will be described later). The revolving body 2 is revolved by being driven by a revolving motor 5 (see FIG. 2 which will be described later).

The work device 3 includes a boom 6 rotatably connected to the front portion of the revolving body 2 , an arm 7 rotatably connected to the tip of the boom 6 , and a rotatable tip of the arm 7 . and a connected bucket 8 . The boom 6, the arm 7, and the bucket 8 are rotated by driving the boom cylinder 9, the arm cylinder 10, and the bucket cylinder 11, respectively.

A cab 12 on which an operator rides is provided on the front left side of the revolving body 2 . Inside the cab 12, there are provided a plurality of operating devices (details of which will be described later) operated by an operator.

The hydraulic excavator drives a plurality of hydraulic actuators (more specifically, the traveling motors 4A and 4B, the swing motor 5, the boom cylinder 9, the arm cylinder 10, the bucket cylinder 11, etc.) according to the operations of the plurality of operating devices. Equipped with a hydraulic drive that The configuration of this hydraulic drive system will be described with reference to FIGS. 2 and 3. FIG. FIG. 2 is a diagram showing a hydraulic pump, hydraulic actuators, control valves, and the like in the configuration of the hydraulic drive system according to the present embodiment. FIG. 3 is a diagram showing an operating device and the like of the configuration of the hydraulic drive system according to the present embodiment.

The hydraulic drive system of this embodiment is driven by a prime mover 13 (specifically, an engine or an electric motor), variable displacement hydraulic pumps 14A and 14B driven by the prime mover 13, and pressure oil from the hydraulic pump 14A. traveling motor 4A and bucket cylinder 11, traveling motor 4B driven by hydraulic oil from hydraulic pump 14B, swing motor 5, optional hydraulic actuator 15, and hydraulic oil from hydraulic pumps 14A and 14B. A travel control valve 16A and a bucket control valve 17 that respectively control the flow of pressure oil from the boom cylinder 9 and the arm cylinder 10, the hydraulic pump 14A to the travel motor 4A, the bucket cylinder 11, the arm cylinder 10, and the boom cylinder 9. , arm control valve 18A, boom control valve 19A, and hydraulic pump 14B to swing motor 5, boom cylinder 9, arm cylinder 10, optional hydraulic actuator 15, and travel motor 4B. A swing control valve 20, a boom control valve 19B, an arm control valve 18B, an option control valve 21, and a travel control valve 16B.

Each control valve is an open-center type, and includes a meter-in opening for supplying pressure oil from the hydraulic pump to the hydraulic actuator, a meter-out opening for discharging the pressure oil from the hydraulic actuator to a tank, and a hydraulic pump. and a bleed-off opening for returning pressurized oil from the tank to the tank. In the neutral position of the control valve, for example, the meter-in and meter-out openings are closed and the bleed-off opening is open to return pressurized oil from the hydraulic pump to the tank. At the switching position of the control valve, for example, the area of the meter-in opening and the meter-out opening increases and the area of the bleed-off opening decreases as the pilot pressure, which will be described later, increases. As a result, pressure oil is supplied to and discharged from the hydraulic actuator, and the flow rate is controlled.

The hydraulic drive system of the present embodiment includes a travel operation device 22A that operates a travel control valve 16A, a travel operation device 22B that operates a travel control valve 16B, boom control valves 19A and 19B, and a bucket control valve. A working operating device 23A for operating the valve 17, a working operating device 23B for operating the arm control valves 18A and 18B and the swing control valve 20, and an option operating device 24 for operating the option control valve 21 are provided. Prepare.

Although not shown, the travel operating device 22A includes an operating lever that can be operated by an operator in the front-rear direction, a first pilot valve that generates a pilot pressure according to the amount of operation on the front side from the neutral position of the operating lever, and a second pilot valve that generates a pilot pressure according to an operation amount on the rear side from the neutral position. Then, the pilot pressure generated by the first pilot valve is output to the pressure receiving portion on one side of the travel control valve 16A to switch the travel control valve 16A from the neutral position to the one switching position. Alternatively, the pilot pressure generated by the second pilot valve is output to the pressure receiving portion on the other side of the travel control valve 16A to switch the travel control valve 16A from the neutral position to the other switching position. As a result, the traveling motor 4A is driven by supplying and discharging pressure oil. The pressure sensors 25A and 25B (manipulated variable detectors) detect the pilot pressures of the first pilot valve and the second pilot valve corresponding to the front and rear manipulated variables of the traveling operating device 22A, respectively.

Although not shown, the traveling operating device 22B includes an operating lever that can be operated by an operator in the front-rear direction, a third pilot valve that generates a pilot pressure according to the amount of operation on the front side from the neutral position of the operating lever, and a and a fourth pilot valve that generates a pilot pressure according to an operation amount on the rear side from the neutral position. Then, the pilot pressure generated by the third pilot valve is output to the pressure receiving portion on one side of the travel control valve 16B to switch the travel control valve 16B from the neutral position to the one switching position. Alternatively, the pilot pressure generated by the fourth pilot valve is output to the pressure receiving portion on the other side of the travel control valve 16B to switch the travel control valve 16B from the neutral position to the other switching position. As a result, the traveling motor 4B is driven by supplying and discharging pressure oil. The pressure sensors 25C and 25D (operation amount detectors) detect the pilot pressures of the third pilot valve and the fourth pilot valve corresponding to the operation amounts of the front side and the rear side of the traveling operating device 22B, respectively.

Although not shown, the work operation device 23A includes an operation lever that can be operated by an operator in the front-rear direction and the left-right direction, a fifth pilot valve that generates a pilot pressure according to the amount of operation on the front side from the neutral position of the operation lever, A sixth pilot valve that generates pilot pressure according to the amount of operation on the rear side from the neutral position of the control lever; a seventh pilot valve that generates pilot pressure according to the amount of operation on the left side from the neutral position of the control lever; and an eighth pilot valve that generates a pilot pressure according to the amount of operation on the right side from the neutral position of the lever. Then, the pilot pressure generated by the fifth pilot valve is output to one side pressure receiving portion of the arm control valves 18A and 18B to switch the arm control valves 18A and 18B from the neutral position to the one side switching position. Alternatively, the pilot pressure generated by the sixth pilot valve is output to the pressure receiving portion on the other side of the arm control valves 18A and 18B to switch the arm control valves 18A and 18B from the neutral position to the other switching position. As a result, the arm cylinder 10 is driven by supplying and discharging pressure oil. The pressure sensors 25E and 25F (manipulated amount detectors) detect the pilot pressures of the fifth and sixth pilot valves, respectively, corresponding to the amounts of operation on the front and rear sides of the work operating device 23A.

The operating device 23A for work outputs the pilot pressure generated by the seventh pilot valve to the pressure receiving portion on one side of the control valve 20 for turning, and switches the control valve 20 for turning from the neutral position to the switching position on one side. . Alternatively, the pilot pressure generated by the eighth pilot valve is output to the pressure receiving portion on the other side of the swing control valve 20 to switch the swing control valve 20 from the neutral position to the switching position on the other side. As a result, the turning motor 5 is driven by supplying and discharging pressure oil. The pressure sensors 25G and 25H (operation amount detectors) detect the pilot pressures of the 11th pilot valve and the 12th pilot valve corresponding to the operation amounts of the left side and the right side of the work operating device 23A, respectively.

Although not shown, the work operation device 23B includes an operation lever that can be operated by the operator in the front-rear direction and the left-right direction, a ninth pilot valve that generates pilot pressure according to the amount of operation on the front side from the neutral position of the operation lever, A tenth pilot valve that generates pilot pressure according to the amount of operation on the rear side from the neutral position of the control lever; an eleventh pilot valve that generates pilot pressure according to the amount of operation on the left side from the neutral position of the control lever; and a twelfth pilot valve that generates a pilot pressure according to the amount of operation on the right side from the neutral position of the lever. Then, the pilot pressure generated by the ninth pilot valve is output to the one side pressure receiving portion of the boom control valves 19A and 19B to switch the boom control valves 19A and 19B from the neutral position to the one side switching position. Alternatively, the pilot pressure generated by the tenth pilot valve is output to the other side pressure receiving portion of the boom control valves 19A and 19B to switch the boom control valves 19A and 19B from the neutral position to the other switching position. As a result, the boom cylinder 9 is driven by supplying and discharging pressurized oil. Pressure sensors 25I and 25J (operation amount detectors) detect the pilot pressures of the ninth pilot valve and tenth pilot valve, respectively, corresponding to the operation amounts of the front side and rear side of the operating device 23B for work.

The work operating device 23B outputs the pilot pressure generated by the eleventh pilot valve to one side pressure receiving portion of the bucket control valve 17 to switch the bucket control valve 17 from the neutral position to the one side switching position. . Alternatively, the pilot pressure generated by the twelfth pilot valve is output to the pressure receiving portion on the other side of the bucket control valve 17 to switch the bucket control valve 17 from the neutral position to the other switching position. As a result, the bucket cylinder 11 is driven by supplying and discharging pressure oil. The pressure sensors 25K and 25L (operation amount detectors) detect the pilot pressures of the 11th pilot valve and the 12th pilot valve corresponding to the operation amounts of the left side and the right side of the work operating device 23B, respectively.

Although not shown, the option operating device 24 includes an operating lever that can be operated by an operator, a thirteenth pilot valve that generates pilot pressure according to the amount of operation on one side from the neutral position of the operating lever, and a neutral position of the operating lever. and a fourteenth pilot valve that generates a pilot pressure according to the operation amount on the other side. Then, the pilot pressure generated by the thirteenth pilot valve is output to one side pressure receiving portion of the option control valve 21 to switch the option control valve 21 from the neutral position to the one side switching position. Alternatively, the pilot pressure generated by the fourteenth pilot valve is output to the pressure receiving portion on the other side of the option control valve 21 to switch the option control valve 21 from the neutral position to the other switching position. As a result, the optional hydraulic actuator is driven by supplying and discharging pressurized oil. The pressure sensors 25M and 25N (operation amount detectors) detect the pilot pressures of the 13th pilot valve and the 14th pilot valve corresponding to the operation amounts of one side and the other side of the option operating device 24, respectively.

The hydraulic drive system of this embodiment includes regulators 26A and 26B that variably control the displacements of the hydraulic pumps 14A and 14B, and a bleed valve that returns pressure oil supplied from the hydraulic pump 14A to the control valves 16A, 17, 18A and 19A to the tank. A bleed-off valve 28A arranged in the OFF pipe 27A, and a bleed-off pipe 27B arranged in the bleed-off pipe 27B for returning pressure oil supplied from the hydraulic pump 14B to the control valves 20, 19B, 18B, 21, 16B to the tank. It includes a valve 28B and a controller 30 that controls the regulators 26A and 26B and the bleed-off valves 28A and 28B via electromagnetic proportional valves 29A and 29B.

The regulator 26A, as shown, has a tilting cylinder for varying the tilting angle of the swash plate of the hydraulic pump 14A, and an electromagnetic valve. This solenoid valve is operated by a pump command current (first command current) from the controller 30 to control the operating pressure of the tilting cylinder. Thereby, the capacity of the hydraulic pump 14A is variable.

The regulator 26B, as shown, has a tilting cylinder for varying the tilting angle of the swash plate of the hydraulic pump 14B, and an electromagnetic valve. This solenoid valve is operated by a pump command current (first command current) from the controller 30 to control the operating pressure of the tilting cylinder. Thereby, the displacement of the hydraulic pump 14B is variable.

The electromagnetic proportional valve 29A is operated by a bleed-off command current (second command current) from the controller 30 to generate and output a bleed-off control pressure. The bleed-off valve 28A is operated by the bleed-off control pressure from the electromagnetic proportional valve 29A, and its opening degree (opening area) is variable.

The electromagnetic proportional valve 29B is operated by a bleed-off command current (second command current) from the controller 30 to generate and output a bleed-off control pressure. The bleed-off valve 28B is operated by the bleed-off control pressure from the electromagnetic proportional valve 29B, and its opening degree (opening area) is variable.

The controller 30, which is the main part of this embodiment, will be described with reference to FIG. FIG. 4 is a block diagram showing the functional configuration of the controller in this embodiment.

Although not shown, the controller 30 has a control section (for example, CPU) that executes arithmetic processing and control processing based on a program, and a storage section (for example, ROM and RAM) that stores programs and processing results. The controller 30 includes, as functional configurations, a pump control section 31A, a bleed-off control section 32A, a reduction coefficient calculation section 33A, and an output section 34A related to the hydraulic pump 14A, a pump control section 31B related to the hydraulic pump 14B, and a bleed-off control. It has a section 32B, a reduction factor calculation section 33B, and an output section 34B.

First, the pump control section 31A, the bleed-off control section 32A, the reduction factor calculation section 33A, and the output section 34A related to the hydraulic pump 14A will be described.

The pump control unit 31A determines the target flow rate of the pump (however, the opening of the bleed-off valve 28A is The target flow rate of the pump that has been corrected as a result of calculation is calculated, the maximum one of the calculated target flow rates is selected, and a pump command current corresponding to this target pump flow rate is generated and output to the solenoid valve of the regulator 26A. .

Based on the pilot pressure detected by the pressure sensors 25A, 25B, 25K, 25L and the pressure sensors 25E, 25F, 25I, 25J, the bleed-off control unit 32A uses, for example, a calculation table shown in FIG. Calculate the bleed-off control pressure. Then, the maximum one of the calculated bleed-off control pressures is selected, and the bleed-off command current corresponding to this bleed-off control pressure is calculated.

The output unit 34A multiplies the bleed-off command current calculated by the bleed-off control unit 32A by the reduction coefficient C calculated by the reduction coefficient calculation unit 33A and corrects it. For example, if the reduction coefficient C=1, the bleed-off command current calculated by the bleed-off control section 32A is output as it is to the electromagnetic proportional valve 29A. In this case, the electromagnetic proportional valve 29A generates the bleed-off control pressure calculated by the bleed-off control section 32A. As the bleed-off control pressure increases, the opening area of the bleed-off valve 28A decreases (see FIG. 6).

The reduction factor calculation unit 33A selects the maximum pilot pressure among the pilot pressures detected by the pressure sensors 25A, 25B, 25K, 25L and the pressure sensors 25E, 25F, 25I, 25J, Decrease speed of the operation amount of the operating device) is calculated. If the pilot pressure Pa was selected at the previous time ta and the pilot pressure Pb (where Pb<Pa) was selected at the current time tb, the rate of decrease in the pilot pressure is (Pa−Pb)/(tb− ta).

The reduction factor calculation unit 33A calculates the reduction factor C from the rate of decrease of the pilot pressure using, for example, a calculation table shown in FIG. Specifically, when the rate of decrease of the pilot pressure is equal to or less than a preset value D (in other words, when there is no possibility that the response delay of the bleed-off valve 28A will increase), the decrease factor C=1. On the other hand, when the rate of decrease of the pilot pressure is greater than the predetermined value D (in other words, when the response delay of the bleed-off valve 28A may increase), 0<C<1 (in this embodiment, 0.2≤ C<1). Also, the reduction coefficient C is reduced as the difference between the rate of decrease of the pilot pressure and the predetermined value D increases. As a result, the bleed-off command current output from the output section 34A to the proportional solenoid valve 29A is reduced, and the bleed-off control pressure generated by the proportional solenoid valve 29A is reduced. As a result, the opening degree of the bleed-off valve 28A can be increased so as to compensate for the response delay of the bleed-off valve 28A.

The reduction factor calculator 33A further limits the speed when the reduction factor C increases. Specifically, when the reduction coefficient C increases, a low-pass filter is used to limit the reduction coefficient C so that the rate of increase of the reduction coefficient C is equal to or less than a predetermined value. Thereby, the opening control of the bleed-off valve 28A can be stabilized.

Next, the pump control section 31B, the bleed-off control section 32B, the reduction factor calculation section 33B, and the output section 34B related to the hydraulic pump 14B will be described.

The pump control unit 31B sets the target flow rate of the pump (however, the bleed-off valve 28A The target flow rate of the pump corrected in consideration of the opening is calculated, the maximum one of the calculated target flow rates is selected, the pump command current corresponding to this target pump flow rate is generated, and the electromagnetic current of the regulator 26B is generated. output to the valve.

The bleed-off control unit 32B uses, for example, the calculation table shown in FIG. , the bleed-off control pressure is calculated from the pilot pressure. Then, the maximum one of the calculated bleed-off control pressures is selected, and the bleed-off command current corresponding to this bleed-off control pressure is calculated.

The output unit 34B corrects the bleed-off command current calculated by the bleed-off control unit 32B by multiplying it by the reduction coefficient C calculated by the reduction coefficient calculation unit 33B. For example, if the reduction coefficient C=1, the bleed-off command current calculated by the bleed-off control section 32B is output to the electromagnetic proportional valve 29B as it is. In this case, the electromagnetic proportional valve 29B generates the bleed-off control pressure calculated by the bleed-off control section 32B. As the bleed-off control pressure increases, the opening area of the bleed-off valve 28B decreases (see FIG. 6).

The reduction factor calculator 33B selects the maximum pilot pressure detected by the pressure sensors 25C, 25D, 25G, 25H, 25M, 25N and the pressure sensors 25E, 25F, 25I, 25J, and reduces the pilot pressure. A speed (that is, a speed at which the operation amount of the operating device decreases) is calculated. Then, for example, the calculation table shown in FIG. 7 is used to calculate the reduction coefficient C from the rate of decrease of the pilot pressure. Specifically, when the rate of decrease of the pilot pressure is equal to or less than a preset value D, the decrease coefficient C=1. On the other hand, when the rate of decrease of the pilot pressure is greater than the predetermined value D, 0<C<1 (0.2≦C<1 in this embodiment). Also, the reduction coefficient C is reduced as the difference between the rate of decrease of the pilot pressure and the predetermined value D increases. As a result, the bleed-off command current output from the output section 34B to the electromagnetic proportional valve 29B is decreased, and the bleed-off control pressure generated by the electromagnetic proportional valve 29B is decreased. As a result, the opening degree of the bleed-off valve 28B can be increased so as to compensate for the response delay of the bleed-off valve 28B.

The reduction factor calculator 33B further limits the speed when the reduction factor C increases. Specifically, when the reduction coefficient C increases, a low-pass filter is used to limit the reduction coefficient C so that the rate of increase of the reduction coefficient C is equal to or less than a predetermined value. Thereby, the opening control of the bleed-off valve 28B can be stabilized.

As described above, in the present embodiment, when the rate of decrease of the pilot pressure (that is, the rate of decrease of the manipulated variable of the operating device) is greater than a predetermined value, the bleed-off rate is higher than when the rate of decrease of the pilot pressure is equal to or less than the predetermined value. The bleed-off command current is corrected so that the opening of the valve increases. As a result, the delay in the response of the bleed-off valve can be improved, and blockage of the pump pressure can be prevented. As a result, the durability of hydraulic equipment such as a hydraulic pump can be improved. Moreover, it is possible to suppress adverse effects on the deceleration or stoppage of the hydraulic actuator (especially the turning motor 5).

Further, by limiting the speed at which the reduction factor C rises, the opening degree control of the bleed-off valve can be stabilized.

A supplementary explanation will be given of the effects of the present embodiment described above. First, the point that the response delay of the bleed-off valve can be improved to prevent the pump pressure from being trapped will be described with reference to FIGS. 8 and 9. FIG. FIG. 8 is a diagram showing temporal changes in the pilot pressure, the bleed-off control pressure, and the opening of the bleed-off valve in the first comparative example (when the bleed-off command current is not corrected). FIG. 9 is a diagram showing temporal changes in the pilot pressure, the bleed-off control pressure, and the opening of the bleed-off valve in this embodiment.

When the operating lever is returned to the neutral position between times t1 and t2, the pilot pressure is reduced. The bleed-off control pressure calculated by the bleed-off control section of the controller 30 also decreases in proportion to the pilot pressure. Then, as shown in FIG. 8, when the command current corresponding to the bleed-off control pressure is left as it is (in other words, the bleed-off control pressure is kept as it is as shown in the figure) and is output from the controller 30 to the electromagnetic proportional valve, the bleed The actual opening of the off-valve increases with a considerable delay. As a result, the degree of opening (opening area) of the bleed-off valve becomes temporarily insufficient, and blockage of the pump pressure occurs.

On the other hand, as shown in FIG. 9, the rate of decrease of the pilot pressure between times t1 and t3 is calculated, a deceleration factor is calculated based on the rate of decrease of the pilot pressure, and the bleed-off command current is calculated using this deceleration factor. is corrected (in other words, the bleed-off control pressure is corrected as shown), and a command current is output from the controller 30 to the electromagnetic proportional valve, the response delay of the bleed-off valve can be improved. Therefore, it is possible to prevent locking of the pump pressure.

Next, the ability to stabilize the opening control of the bleed-off valve will be described with reference to FIGS. 10 and 11. FIG. FIG. 10 is a diagram showing temporal changes in the pilot pressure, the reduction factor, the bleed-off control pressure, and the theoretical opening of the bleed-off valve in the second comparative example (when the speed is not limited when the reduction factor increases). . FIG. 11 is a diagram showing temporal changes in the pilot pressure, the reduction factor, the bleed-off control pressure, and the theoretical opening of the bleed-off valve in this embodiment.

A reduction coefficient C1 is calculated based on the rate of decrease of the pilot pressure between times t1 and t3, a reduction coefficient C2 is calculated based on the rate of decrease of the pilot pressure between times t3 and t4, and between times t4 and t5 When the deceleration factor C3 is calculated based on the rate of decrease of the pilot pressure at time t5 to t6, and the deceleration factor C4 is calculated based on the rate of decrease of the pilot pressure between times t5 and t6, and the relationship C2>C4>C3>C1 holds assume. In this case, particularly at time t4, there is a significant rise from the reduction factor C1 to the reduction factor C2. Therefore, as shown in FIG. 10, if the bleed command current is corrected using the reduction coefficient C2 as it is and output from the controller 30 to the electromagnetic proportional valve, the opening of the bleed-off valve becomes unstable. On the other hand, as shown in FIG. 11, the degree of opening of the bleed-off valve can be stabilized by suppressing the speed when increasing from the reduction factor C1 to the reduction factor C2.

In the above-described embodiment, when the rate of decrease of the pilot pressure (that is, the rate of decrease of the manipulated variable of the operation device) is greater than the predetermined value D, the controller 30 multiplies the bleed-off command by a reduction coefficient C smaller than 1. Although the case of correcting the current has been described as an example, the present invention is not limited to this and can be modified without departing from the gist of the present invention. For example, the controller may correct the bleed-off command current by subtracting a correction amount greater than 0 when the rate of decrease of the pilot pressure (that is, the rate of decrease of the manipulated variable of the operating device) is greater than a predetermined value. In this modification, the correction amount may be increased as the difference between the speed of decrease of the pilot pressure and the predetermined value increases. Also, the speed at which the correction amount decreases may be limited.

In the above embodiment, the hydraulic excavator includes electromagnetic proportional valves 29A and 29B that are operated by the bleed-off command current from the controller 30 to generate the bleed-off control pressure. Although the case of operation by the bleed-off control pressure from the valves 29A and 29B has been described as an example, the present invention is not limited to this, and modifications are possible without departing from the gist of the present invention. For example, the bleed-off valve may be actuated by command current from the controller.

In the above embodiment, the hydraulic excavator includes, as an operation amount detector, a pressure sensor that detects the pilot pressure corresponding to the operation amount of the operating device. Modifications are possible without departing from the gist of the invention. The hydraulic excavator may include, as the operation amount detector, for example, a displacement sensor that detects the operation amount of the operation lever.

In the above description, the hydraulic excavator is used as an example of the application of the present invention, but the present invention is not limited to this, and may be other working machines such as wheel loaders.

Reference Signs List 1 traveling body 2 swinging body 3 work device 4A, 4B travel motor 5 swing motor 9 boom cylinder 10 arm cylinder 11 bucket cylinder 13 prime mover 14A, 14B hydraulic pump 15 optional hydraulic actuator 16A, 16B travel control valve 17 bucket control valve 18A, 18B Control valve for arm 19A, 19B Control valve for boom 20 Control valve for turning 21 Control valve for option 22A, 22B Operation device for traveling 23A, 23B Operation device for work 24 Operation device for option 25A to 25N Pressure sensor (operation quantity detector)
26A, 26B regulator 27A, 27B bleed-off pipeline 28A, 28B bleed-off valve 29A, 29B electromagnetic proportional valve 30 controller

Claims (4)

a hydraulic actuator;
a variable displacement hydraulic pump driven by a prime mover;
an open-center type control valve that controls the flow of pressure oil from the hydraulic pump to the hydraulic actuator;
an operating device for operating the control valve;
an operation amount detector that detects an operation amount of the operation device;
a regulator that variably controls the displacement of the hydraulic pump;
a bleed-off valve disposed in a bleed-off pipeline for returning pressure oil supplied from the hydraulic pump to the control valve to a tank;
for outputting a first command current for controlling the displacement of the hydraulic pump and for controlling the opening of the bleed-off valve according to the operation amount of the operating device detected by the operation amount detector; A working machine comprising a controller that outputs a second command current,
an electromagnetic proportional valve operated by the second command current from the controller to generate a bleed-off control pressure;
The bleed-off valve is operated by the bleed-off control pressure from the electromagnetic proportional valve, and the opening area decreases as the bleed-off control pressure increases,
The controller is
using the operation amount of the operation device detected by the operation amount detector, calculating the rate of decrease of the operation amount;
a reduction factor smaller than 1 so that when the rate of decrease of the manipulated variable is greater than a predetermined value set in advance, the bleed-off control pressure becomes smaller than when the rate of decrease of the manipulated variable is equal to or less than the predetermined value; A working machine characterized in that the second command current is corrected by multiplying by . The work machine according to claim 1 ,
A working machine, wherein when the rate of decrease of the manipulated variable is greater than the predetermined value, the controller reduces the reduction factor as the difference between the rate of decrease of the manipulated variable and the predetermined value increases. In the work machine according to claim 2 ,
The working machine, wherein the controller limits the speed when the reduction factor increases. The work machine according to claim 1,
a traveling body, a revolving body rotatably provided above the traveling body, and a working device connected to the revolving body;
A working machine, wherein the hydraulic actuator includes a plurality of swing motors for swinging the swing structure.

Images